Seasonal affective disorder (SAD) is a well-established mood disorder wherein sufferers experience depressive symptoms in a certain season of the year, most frequently during the winter months. Those affected by SAD often have normal mental health during most of the year. Symptoms of SAD may include, but are not limited to, excessive sleeping, lack of energy, craving carbohydrates, difficulty concentrating, and withdrawal from social activities. The symptoms result in feelings of depression, hopelessness, pessimism, and lack of pleasure.
Seasonal mood variations are believed to be related to changes in exposure to light. Individuals in geographic areas, such as the Arctic region, that experience fewer daylight hours, lower sunlight intensity, or significant periods of overcast skies exhibit a greater incidence of SAD. Variations in prevalence of SAD within the adult population are evident within the United States, ranging from low rates in Florida and other sunny states to notably higher rates in Alaska, New Hampshire and other northern or overcast areas.
Light therapy has been researched and established as a prominent and effective treatment for classic, or winter-based, seasonal affective disorder. Conventional light therapy employs a device which emits significantly more lumens than a standard incandescent lamp. Common implementations include the preferred bright white full spectrum light at 10,000 lux, or optionally blue light at a wavelength of 480 nm at 2,500 lux, or green light at a wavelength of 500 nm at 350 lux. Light therapy normally requires a patient to sit with their eyes open at a prescribed distance from the light source for thirty to sixty minutes each day. This seasonal treatment is maintained for several weeks until the patient experiences frequent exposure to natural light. A majority of patients find the existing therapy inconvenient and a considerable percentage, in some studies up to 19%, therefore stop the treatment. New methods and approaches are therefore desirable to deliver light therapy in more convenient, controlled, and intelligent manners.